Batteries are used in many assemblies, such as in vehicles, to provide electrical power to the various components and/or devices which cooperatively and respectively form these assemblies. It is highly desirable to accurately and continually measure and/or ascertain the electrical charge remaining within the battery, commonly referred to as the "state-of-charge", in order to ensure that the battery is timely and efficiently recharged or replaced, and to further ensure continued and substantially uninterrupted operation of the vehicle or other type of "battery powered" assembly. Consequently, many devices have been developed and have been used to selectively measure the state-of-charge of a battery and to selectively display the measured state-of-charge to a user of the battery powered assembly.
These prior state-of-charge measuring devices typically include an electrical current integrator (e.g., a capacitor) which is connected to the battery in an "electrical series" arrangement or manner, and which operatively integrates the electrical current which is provided by the battery. Particularly, this electrical current is coupled to and made to traverse the device. The device, in this manner, calculates the amount of electrical charge which has passed into the device due to the received electrical current. Particularly, this calculation is accomplished by measuring the voltage and/or the charge of the capacitor (i.e., the integral of the electrical current which has been received by the device during a certain time interval is substantially equal to the electrical charge which is accumulated upon and/or by the contained capacitor during this time interval). Similarly, this device measures the amount of electrical charge which is provided to the battery and the summation of these charges (i.e., the charges respectively provided by and provided to the battery) provides an accurate indication of the current state-of-charge of the battery.
As noted, many of these prior devices perform these calculations by measuring the voltage which is applied to and/or which is received by the capacitor from the battery, after a certain interval of time has elapsed, by the use of the equation: Q=V*C, where "Q" equals the amount of electrical charge accumulated by the capacitor or the integral of the electrical current which passes into the capacitor during the interval of time, "V" equals the voltage across the capacitor at the end of the interval of time, and "C" equals the capacitance value of the capacitor. In order for the foregoing calculation to be accurate, there must be substantially no voltage across the capacitor at the beginning of each measured time interval. Moreover, these calculations and/or measurements should be initiated as soon as the fully charged battery is operatively placed into the assembly.
These prior devices typically "conduct" or make these measurements over consecutive intervals of time and add these measurements together to determine the total electrical charge which has passed into and/or out of the battery. That is, by subtracting the total electrical charge which has passed out of the battery from the battery's total electrical charge capacity and then by adding the total electrical charge which has passed into the battery, a relatively accurate and current estimate of the battery's remaining charge is provided. A "running total" of the electrical charge remaining in the battery or the battery's "state-of-charge" is typically stored within the memory of these devices and is selectively displayed to a user of the vehicle or other battery powered device. While these state-of-charge measuring devices do effectively maintain and display the state-of-charge of a battery, they suffer from some drawbacks which undesirably reduce their respective accuracy.
For example and without limitation, while the capacitors employed by these prior devices effectively and respectively integrate the electrical current flowing into and/or out of the battery over a discrete interval of time, the capacitors eventually reach their respective charge storing capacity limit and must be "reset" or electrically discharged before continuing to integrate or further accumulate any more electrical charge. Discharging these capacitors requires some finite period of time, which is usually dependent upon the size of the capacitor.
While these capacitors are being discharged, the battery continues to operate (i.e., continues to provide and/or receive electrical current) and the concomitant change in the state-of-charge of the battery is not detected or measured by these devices (i.e., these devices are inoperable). Thus, this "unmeasured electrical current" is not factored into the "running total" kept by these devices, thereby causing these devices to produce inaccurate and/or erroneous "state-of-charge" estimates.
Attempts have been made to mathematically estimate the "unmeasured electrical current" using conventional mathematical extrapolation techniques. While these extrapolation techniques have been shown to somewhat reduce the overall error, they are not highly accurate and often result in the creation of relatively small errors which accumulate over time, causing the creation of relatively large undesirable state-of-charge measurement errors. These techniques further add undesirable complexity to these prior state-of-charge devices.
Additionally, the capacitance values of these capacitors often drift or vary over time. Any uncompensated variance in these capacitance values will cause these prior devices to further provide inaccurate state-of-charge measurements. In order to correct for these variances, efforts have been made to calibrate these devices and/or to measure the value of these capacitors at regular and/or discrete intervals of time, and to thereafter selectively compensate for the measured variances. However, while these devices are being calibrated, no measurement is made of the electrical current flowing into and out of the battery, thereby further increasing the state-of-charge measurement error.
There is therefore a need for a new and improved state-of-charge measuring device which provides a relatively accurate measure or estimate of the state-of-charge of a battery; which continuously measures or integrates the electrical current passing into or out of a battery; and which continues to integrate and/or measure electrical current while the device is being reset, discharged, and/or calibrated.